Category:Acetylcholinesterase



 3D structure of acetylcholinesterase

Key Enzyme in the Nervous System
Acetylcholinesterase (AChE) is key enzyme in the nervous system of animals. By rapid hydrolysis of the neurotransmitter, acetylcholine (ACh), AChE terminates neurotransmission at cholinergic synapses. It is a very fast enzyme, especially for a serine hydrolase, functioning at a rate approaching that of a diffusion-controlled reaction. AChE inhibitors are among the key drugs approved by the FDA for management of Alzheimer's disease (AD). The powerful toxicity of organophosphorus (OP) poisons is attributed primarily to their potent AChE inhibitors.

The 3D structure of Torpedo californica AChE (TcAChE) (Sussman et al. & Silman (1991)) opened up new horizons in research on an enzyme that had already been the subject of intensive investigation. The unanticipated structure of this extremely rapid enzyme, in which the active site was found to be buried at the bottom of a deep and narrow gorge , lined by aromatic residues, led to a revision of the views then held concerning substrate traffic, recognition, and hydrolysis (Botti et al. Sussman & Silman (1999)).

Alzheimer’s disease (AD) is a debilitating brain disease that occurs in around 10% of the elderly and, as yet, there is no known cure. At present, the most widely used treatments consist are medications that attempt to increase the brain’s levels of ACh, whose levels decrease with onset of disease. These drugs work by interfering with AChE. Thus drugs that are mild inhibitors of AChE, like Tacrine, E2020 (Aricept) and the Traditonal Chinese Medicine (TCM) Huperzine appear to retard symptoms of AD.

two binding sites, a catalytic site (consisting of the catalytic triad together with Trp84 & Phe330) and a peripheral site (including Trp 279 & Tyr 121), which helps prebind the substrate and direct it toward the active site. The 3D structure showed not only that the active site was buried deep in the enzyme, but surprisingly, there were no negatively charged residues along this gorge, as was expected to help attract the positively charged ACh substrate, rather, instead, a series of aromatic residues that are highly conserved  in all AChE sequences. See: AChE inhibitors and substrates

Selected 3D Structures of AChE

 * 2ace This is the original solved structure for T. californica
 * 1ea5 This is the highest resolution X-ray structure of AChE determined till now.
 * 1eve The E2020 (Aricept) complex.
 * 1ax9 Edrophonium complex.
 * 1vot Complex with huperzine, a traditional Chinese folk medicine.
 * 1fss Complex with the snake venom toxin, Fasciculin-II.
 * 1vzj Model complex of the cholinesterase tetramer.
 * 1som Complex with nerve agent soman (GD).

More structures can be obtained by searching for AChE